MEAT MICROBIOLOGY
1 MICROOGANISMS OF SLAUGHTER ANIMALS:
2. MICROORGANISMS AT SLAUGHTERING PROCESS:
Pre-mortem inspection should remove from slaughter excessively dirty and obviously diseased animals. However, inspection cannot prevent slaughter of stock carrying human pathogens in the intestinal tract or on the hide or fleeces .During slaughter and dressing, head, hide or fleece hocks and viscera are removed. These operations are important. The object is to do this with as little contamination as possible of the exposed sterile carcass tissue and of edible offal. The rumen, lower intestinal tract and the hide and fleece all carry very large numbers of microorganisms.
Faeces may contain up to 106 spores of Cl. perfringens
/
g (smith,1961) as well as salmonellae at levels of up to108 /g, C.jejuni, and
L.monocytogenes (table, 6). In the faeces of healthy bobby calves there
can be 106 viable cells of C.jejuni, though numbers are fewer in more
adult animals (Gray, 1988). Rumen fluid may contain salmonellae and
C.jejuni in low numbers. The hide and fleece can carry considerable
numbers of salmonellae. Patterson and Gibbs (1978) found up to 4×106
salmonellae/g on cattle hair, and 200 salmonellae/cm2
on sheep fleece
(Gray and Smith, 1974). Listeria monocytogenes also could be on hides and fleeces (Lowry and Tiong, 1988). Yeast (e.g. Candida Cryptococcus and Rhodotorula spp.) usually form only a small percentage of the microflora but can be as high as 12.7% of the microbial load (Dillon and
Board, 1991). Hooves usually also carry a large microbial population. Scrapings from cattle hooves yielded 260 Salmonellae/g. A high percentage of Staph.aureus strains from mastatic goats, sheep and cattle were reported.
The equipment used in the slaughter-dressing operation, and the hands and clothing of personnel can contaminate and spread contamination from animal to animal.
Unless properly cleaned, saws, steel-mesh knives and other equipment carry a high bacterial load and can be sources of contamination. Intestinal tract material (rumen and lower intestine) is most likely to be the major source of E. coli, Salmonellae, C.jejuni, Cl. Perfringens and other Clostridia for carcass and offal.
Hide and fleece add most of the mesophilic aerobic (including bacilli) and the psychrotrophic (including psychrotrophic yeasts) to the carcass, the skin is also a source of Staphylococci, L.monocytogenes and
Clostridia.
The extent and nature of contamination of carcass and offal meat are reflections of the microbial status of the animal as presented for slaughter, and the care and standards of hygiene and sanitation used, (ICMSF, 1998). Chilling of carcasses and offal prevent growth of mesophilic pathogens and reduce the growth rate of psychophysics pathogens and spoilage organisms.
Slaughter:-
After animals are stunned they fall to the floor where the hide can pick up faecal contamination, the hide of calves and cattle can acquire salmonellae or C.jejuni, there can also be increases in the incidence of
L.monocytogenes on cattle hide after stunning, and this organism has
been found on the floor of stunning area.
It is possible for bacteria on the instruments used in slaughtering to contaminate some deep tissues through the blood stream (Mackey and Derrk, 1979). When the end of captive blot, heavily coated with bacteria, penetrated the skull of cattle, the organism could be recovered from the spleen but not from muscle. When cattle were pithed with heavily contaminate pithing rods, bacteria were found in the spleen and, at times in muscles of the neck and flank. Bacteria from inoculated stick-knives
(108-1011 cells) were isolated from the blood and some times from the
heart, liver, kidney, spleen and lung of sheep, though rarely from muscles. With relatively modest hygiene it is unlikely that muscle is often contaminated by either the stick – knife or captive bolt. After the neck skin of cattle is cut, the knife is decontaminated before the carotid blood vessels are severed. The relative ease with which sterile muscle can be obtained for experimental purposes from normal animals suggests that muscle is essentially sterile.
Inadequate bleeding of carcasses at slaughter and the blood content of muscle appears to have no effect on microbial growth on meat or the keeping quality (Gill ,1991) though this might not be true as seen by
other researchers (P.Sanosi, personal contact). The Oesophagus is cleared from surrounding tissue and tied or clamped close to the ramen to prevent leakage of rumen fluid which would contaminate the neck and, during evisceration, the pleural region with bacteria .Contamination from lower–intestinal tract material is more of a hazard – due to higher level of Enterobacteriaceae.
Skinning:-
Most of the microbial load on the carcass is derived from the skin, hide or fleece during skinning. Bacterial contamination includes the normal skin flora as well as organisms from soil and faeces which are on the skin , and includes Yeasts, Bacilli Micrococci, Staphylococci,
Corynibacteria, Moraxella, Acinetobacter, Flavobacteria, Enterobacteriaceae , E. coli ,Salmonellae and Listeria spp, ( ICMSF,
1998) . In New Zealand, cattle hide and sheep fleece appear to be the major source of L.monocytogenes on the carcass (Lowry and Tiong, 1988). The predominant contamination is mesophilic the percentage of psychrophiles varies with season and geographic location. Some times animals are washed before slaughter to remove loose dirt; however it is not clear whether per-slaughter washing has any significant effect on microbial contamination of carcass (Roberts, 1980, Gill, 1990).
Hocks are removed and incisions through the skin are made along the inside of the legs, along the neck, sternum and abdomen and around the anus. Knives and operator's fist are used to separate the skin from the underlying hock and skin become heavily contaminated, as do their
knives, steels and clothes. Salmonellae can often be found on the hands and equipments of these workers (Smeltzer et al, 1980, Stolle, 1981). In one study in Germany, the highest contamination of carcasses with salmonellae was associated with removal of hooves and freeing of skin around the legs (stolle, 1981) L.monocytogenes has been found on the knives and hides (Gobat and Jemmi, 1991). The incision through the contaminated skin carries microorganisms on-to the carcass tissue. The knife blade and handle and the hands of the operator –as these are used to free the skin– transfer organisms mechanically onto the carcass. Bacterial numbers are highest on region of the carcass where the initial manual removal of the skin takes place and lowest where skin is mechanically pulled away (Kelly et al., 1980). The brisket is a site, which is usually considered a dirty site in terms of total bacterial contamination. Organisms are also transferred to the carcass when fleece or hide contact tissue, or when exposed tissue, is handled by operators. Cutting the skin around the anus and freeing the anal sphincter and rectal end of the intestine are major source of carcass contamination with
E. coli and salmonellae, and presumably also with C.jejuni. The hide and
skin around the tail are often contaminated with faeces. Care taken during this operation is critical in limiting faecally derived contamination. Samples taken immediately after tissue was exposed during hide removal showed that there was considerable more contamination with E.coli and salmonella of the perianal and rectal channel than of hind–leg or brisket. The rectal end of the lower intestinal
tract of beef animals is often enclosed in a plastic bag to limit contamination of the rectal channel and abdominal cavity. During subsequent carcass trimming some of the contamination on the fatty tissues around the anal opening is removed. In the operation of releasing the anal sphincter and rectum of sheep, the operator may handle the anus, and with his hand then handle the exposed tissues of the hind leg. After the anal sphincter and the rectum are cut free, there can be about 100–fold increase in E. coli and a significant increase of Salmonellae on sheep carcasses without any detectable increase in the total aerobic viable count (Gray, 1986).
During mechanical hide pulling on cattle, the intestine may be occasionally squeezed through cuts in the abdomen, made from the initial knife incision, and the intestine may rupture contaminating the abdomen and chest regions.
Evisceration:
As part of the evisceration process, the brisket is cut, the abdomen is opened, and the organs of the thorax and abdomen are removed. Offals are separated from the viscera and inspected. Care is needed to prevent puncture of the rumen during brisket cutting.
Similarly, use of the correct style of knife and care by eviscerator to prevent the knife piercing the rumen or intestinal tract is needed. Puncture of intestine or spillage of its content can cause massive contamination of the carcass and offals.
Compylobacter can occur in bile (Bryner et al. 1972). The gall–
bladder and mesenteric and hepatic lymph nodes can be infected with salmonellae (table 10). Normally, salmonellae are found in less than 10% of these lymph nodes. However in cattle and sheep held for some days in contaminated abattoir environments more than 50% of jejunal, caecal and colonic lymph nodes can harbour Salmonellae (Samuel et al, 1981), be more than 7500 Salmonellae/g of mesenteric, nodes (Samuel et al., 1980). In cattle where there was a high incidence and a high count of salmonellae in these nodes draining the lower intestine, infections of the tonsils, retropharyngeal, rumenal and abomasal nodes were rare.
Salmonellae were also not found in the tracheobronchial, caudal
mediastinal, lumbar aortic, medial iliac, superficial inguinal or caudal deep cervical lymph nodes. In spite of a high infection rate of mesenteric lymph nodes, spread beyond is limited. Organisms that spread systematically appear to be localized in the spleen or liver. Following
intranasal inoculation of sheep with Salmonellae (103-104 cells),
Salmonellae could be isolated from lymph nodes of the head and neck
region of some infected animals (tonsil, suprapharyngeal, mandibular, parotid and bronchial nodes (Tannock and Smith, 1971).
Incision of lymph nodes can contaminate the hands knives of veterinary inspectors and salmonellae can then spread to edible tissues. Requirements for lymph node incision have been considerably reduced in recent years. Though salmonellae are occasionally present inside livers, significant contamination of the liver surface occurs during
evisceration and separation from other viscera, and from the hands and knives of veterinary inspectors (Thomas, 1981). Livers and offals become contaminated also with C.jejuni. General contamination of the heart, liver and diaphragm of cattle and sheep has been shown to take place during removal from carcass cavity, from contact with the evisceration table, and from handling during separation of the different organs (Sheridan and lynch, 1988).
Trimming and washing:-
Trimming and washing are done to improve the appearance of the
carcass and remove blood, bone dust, hair and soil. Trimming will remove some bacterial contamination, washing remove some bacteria and redistributes some organisms from one site to another. The effectiveness of washing varies with temperature, pressure, and volume of water and the design of the system and time spent.
Washing with water at less than about 40-50co tends to give
relatively small and variable reductions in bacterial contamination. Counts at more highly contaminated sites may be reduced, while counts are unchanged at sites with an initial low level of contamination (Kelly et al, 1981). Sheridan (1982) obtained a reduction of 60-fold in the microbial load on sheep carcasses, but the mean initial counts on the
sites sampled appear to be high (log10 x 4.6-4.9/cm
2). Raising the
temperature of the wash water above 800c tends to give a better
reduction in carcass contamination, but even then the reduction may be small (Patterson, 1968).When a spray system is used to wash carcasses,
there is a marked fall in the temperature of the water after it leaves the nozzle. When the temperature of sprayed water at impact on the carcass
is 56-63oC, the psychrotrophic population is reduced about 10-fold. At
impact temperatures of 65oC , the reduction in the mesophilic load still
tends to be variable (log10 x0.2-09). Impact temperatures of 80
oC and
above appear to be needed to give at least a 10-fold reduction in the numbers of mesophiles on carcasses (Kelly et al; 1981).
For hot water to be effective, all surfaces of the carcass need to be contacted for sufficient time. Though immersion in water at 80co for 10 seconds seems to achieve this and reduces the coliform and mesophilic count on the carcasses by between 10 and 100 fold, but is not a practical procedure. An automatic hot water wash–cabinet designed to distribute a continuous stream of water over all surfaces of a beef-side and prevent heat and vapour loss to the environment, can give more than more than a
log10 2 reduction in numbers of E.coli on the surfaces of beef sides
(Smith and Davey, 1990). Experiment with this system show that the temperature of the film of water at the carcass surface must be above
55oC for there to be any significant lethal effect.
The addition of chlorine to wash water appears to have only a small effect on reduction of contamination (Kelly et al; 1981). Normally there is not more than a five-fold reduction in microbial count. Low concentrations of chlorine (20-30mg/L) give some reduction which is not markedly changed with increasing chlorine concentration. Populations of E. coli on beef were not significantly reduced by 800
ppm chlorine (Cutter and Siragusa, 1995). Both acetic and lactic acid solutions, when applied to carcass surfaces, reduced bacterial contamination. A 1% solution of lactic acid reduced the mesophilic
count on beef, veal and pork carcasses between log10 0.8 and 1.9. Both
acetic and lactic acids have a residual affect, reducing the rate of microbial growth on chilled meat. However, acid sprays appear to produce little reduction in E.coli and Salmonella on meat surface (Brackett et, al. 1994).
Normally, washing has only a small effect on the overall microbial load on the carcass. If special systems are used (such as water at high impact temperature, lactic or acetic acid solution), significant reduction in bacterial contamination is possible. In such a case, temperature, time of application, concentration and/or volume will need to be controlled to ensure efficient operation of the system.
Table (8): Bacterial numbers on beef carcasses before chilling
EEC country a 1 2 3 4 5 6 7
Survey 1
Mean log10 CFU/cm2 (30oc) 3.85 2.77 2.29 3.14 2.45 2.75 3.23
Enterobacteriaceae (%+V) 74 67 39 79 47 79 61
Survey 2
Mean log10 CFU/cm2(30oc) 3.78 3.15 2.35 3.50 2.48 3.11 3.33
Norwayb 1 2 3 4 5 6 7 8 9
Mean log10 CFU/cm 2
(20oc) 2.46 2.24 2.87 2.09 2.56 2.42 2.36 1.98 2.23
Englandc 1 2 3 4 5 6 7 8
Mean log10 CFU/cm 2
(37oC) 2.68 2.98 1.83
Mean log10
CFU/cm2(20oC/30oC)
3.12 2.95 2.03 3.03 3.06 3.60 3.57 3.76
Mean log10 CFU/cm 2
(1oC) 1.96 1.83
Enterobacteriaceae (% +ve) 19 66 70
Coliforms (% +ve) 17 19
Other countries NZ In1 In2
Mean log10 CFU/cm 2
(25oC) 1.85 3.62 4.02
Mean log10 CFU/cm 2
(0oC) 0.56
Coliforms (%> 10/cm2) 77.3 85.7
Salmonella (%positive) 15.5 13.6
a = Samples obtained at seven countries. b = Samples obtained at nine abattoirs. c = Samples obtained at eight abattoirs.
NZ=New Zealand. In = India. (ICMSF, 1998)
Cattle and sheep carcasses, at completion of hygienic slaughter and
dressing, can typically have on their surface tissues about 102-104
mesophiles/cm2. (Tables 8 and 9). Count consistently above
about105/cm2 indicates that more care is needed in carcass dressing
(Mackey and Roberts 1993). A large proportion of the organisms are Gram-positive (e.g. micrococci. staphylococci, coryniforms). enterobateriaceae and coliforms can be detected (table 8 and 9) usually in small numbers (e.g. only 2% of 182 swab samples from beef
carcasses had more than 11 CFU of enterobacteriaceae/cm2. Potential
pathogens that may be present include Salmonella spp enteroheamorrhagic.E.coli; C.jejuni; Staph.aureus; L.monocytogenes;
B.cereus; Cl.Perfringens and occasionally Cl.botulinum. The
psychrotrophic population will have a variable percentage (from about 0.2-10%) of the mesophilic count. The proportion of psychrotrophs varies with ambient temperature so that there will be both seasonal and geographical differences. Psychrotrophs that may be found on carcasses
include Pseudomonas, Acinetobacter, Psychrobacter,
Enterobacteriaceae, Broch. thermosfacta, lactic acid bacteria and yeasts
Table (9): Bacterial numbers on sheep carcasses before chilling
a =Abattoirs in England. Samples obtained by wet-dry swabbing of 100 cm2 at each of 10 sites on each carcass. Aerobic viable count determined by incubation at 37°,
20° and 1°C. Mean log10 number is the mean log10 values for all sites (Roberts et
al., 1980b).
b =Abattoir in Ireland. Samples obtained by wet swabbing of 25 cm2 at each of 12 sites on each carcass before spray washing (Kelly et aI., 1980).
c =Abattoir in New Zealand. Samples obtained by wet swabbing of 10 cm2 at two sites on each carcass (Newton et al., 1978).
d =Abattoir in Australia. Samples obtained by dry swabbing of 100 cm2 at each of 10 sites on each carcass immediately after spray washing (Gray, 1978).
e =Aerobic viable count determined by incubation at 25°C. f =Aerobic viable count determined by incubation at O°c.
g =Mean log10 CFU E. coli/ cm2.
h =Abattoir in Spain. Samples obtained by swabbing, and excision of the swabbed
Abattoir Ela E2a E3a E4a E5a E6a lrelb NZc Austd Sph Mean log 10 CFU/cm2 (37°C) 3.18 3.01 2.5 4 2.8 4 3.2 5 2.76 Mean log 10 CFU/cm2 (30°C) 4.96 Mean log 10 CFU/cm2 (20°C/25°C) 3.45 3.13 2.67 2.90 3.32 3.13 3.77e 2.78e 3.18e Mean log10 CFU/cm2 (7°C) 4.48 Mean log10 CFUlcm2 (1°C) 2.13 O.77 f Enterobacteriace ae (% positive) 57 48 69 Coli forms (% positive) 44 28 18 59 (0.99) g No. carcasses 18 6 6 12 6 6 7 29 10 8
and scrapped areas of 45 cm2 at each of the three sites on each carcass (Prieto et al., 1991).
One survey of dressed camel carcasses (Hamdy, 1981) found
counts of 3.6x105 mesophiles, 4.8x103
Enterobacteriaceae. And 2.2 x103 Staph. aureus /cm2.
Offal can have on surface about 103-105 mesophiles/cm2
(Table 13)
The flora on offal is similar to that on carcass, being mainly Gram- positive, but Enterobacteriaceae can be a significant percentage of the initial flora (Oblinger et al., 1982). Several hundred bacteria per gram can be found in the internal tissue of liver. Internal tissues of the open sinusoidal structure of organs like liver can be contaminated during organ removal from the carcass (Gill, 1988).
Table (10). Bacterial counts (log10 CFU/cm2) on offal before chilling: Tail Tongue Diaphragm Kidney Heart liver Species - 5.99 6.46 3.73 3.72 4.35 Beef 4.45 4.97 4.86 - 4.58 5.51 4.86 4.98 3.75 4.72 4.61 4.55 - - - 2.77 2.28 2.50 - 3.69 - - - 3.36 - 4.20 - 3.51 3.92 3.69 - 3.61 - 3.66 3.85 3.58 - 2.32 - 2.85 3.13 2.61 - 6.38 5.46 - 4.92 4.62 sheep - - - 3.29 3.05 4.23 - 4.28 - - - 3.18 - - - 3.80 3.04 3.28 pig - 5.76 - - - 4.04 - - - - - 4.78 - - - - - 3.28 - - - - - 3.27 (ICMSF, 1998) - - - 1.60
Chilling:
Chilling is a critical control point in the (HACCP) system. Adequate chilling prevents the growth of thermophilic and mesophilic pathogens (e.g. salmonella), and limits growth of Psychrotrophs.
Carcasses of sheep & young calves and sides of beef are chilled in
air. Air temperatures are usually maintained-except for the period during
loading of the chiller-at less than 7-8oc. The temperature used depends
on the species and subsequent stages of production. If beef or sheep is to be taken directly from slaughter house-at least 18-24 hours from
slaughter air temperatures below 7oc are used. If the meat is for chilled
or frozen trade as carcasses, sides or quarters, it is often chilled with air
near -1 to 2oc. Rapid chilling causes cold-shortening and toughening of
meat (lawrie 1991). This is largely prevented by electrical stimulation after stunning.
Table (11): Bacteria on chilled beef carcasses:
Result No. of carcasses examined
Organism
93.1 % < 104/cm2
2089